The present invention relates generally to a connection system between input devices and detector modules. More particularly, the present invention relates to a connection system between input detectors on a vehicle steering wheel and detector modules on a column side of a vehicle steering system.
Modern vehicles are requiring more and more user-input functions. These functions include switches for cruise control, radio, tape player, compact disk player, windshield wipers, seat positioning, electric mirrors, heating, ventilation, air conditioning, and rear window defogger, just to name a few. Many of these functions are located on switch pods or in the steering wheel. Typically the input is in digital form to provide high-resolution and simplicity. Even microphones and speakers are becoming a desired feature for phone usage. Connection to and from these inputs is creating a huge demand on the design configurations to accommodate the large amount of inputs over limited connections.
Wire bundles are becoming larger to accommodate more and more circuits that are being added. Furthermore, the size of individual wires cannot decrease due to the requirements of mechanical strength and durability. Each additional circuit adds weight and cost due to the additional module interconnect components and wires. Multiplexing and communication busses have provided some relief in limiting the size increases in connection components. However, the requirements of more sensor circuits, reduced vehicle weight, reduced costs, and reduced free space for components, are adding additional pressure to maximize the number of inputs that can be handled by each connection.
A typical example of the need to maximize inputs available per connection is in the steering column wherein a ribbon tape conductor, called a clockspring for its resemblance to a wound clock spring, is used to couple steering circuits to the steering column of the vehicle. As the circuit count increases, the ribbon tape of the clockspring thickens in conventional practice to accommodate the additional circuits. Eventually, however, there will be no more room available to accommodate an ever increasing clockspring. This area is further challenged by complex suspension controls being added to new car designs, and these suspension controls must share the same location in the steering column as the clockspring in order to function properly, and needed additional space is not available.
Prior art connection methods typically include one of the following three methods of passing signals to a module. The first method uses a single wire connection for each input device. The second method uses a simplified multiplexing scheme usually incorporating analog voltage, resistance or current division means. The third method uses a communication bus, which requires a microprocessor on both ends of the conductor.
While a communication bus can handle a large number of input devices per connector, such a design requires a plurality of microprocessors which makes the system expensive to produce. Furthermore, a communication bus requires a communication chip for line drive and receive functions. A communication bus also utilizes a lot of circuit board space, which makes the system expensive to produce.
Accordingly, there is a need for multi-input communication system over a single line that is more compact and cost effective.
A first object of the present invention is to increase the number of input devices that can be accommodated over a single connection line.
A second object of the present invention is to reduce the manufacturing cost of a connection system.
A third object of the present invention is to reduce the total number of individual wires between multiple input devices and receiving modules in a connection system.
A fourth object of the present invention is to reduce the weight of a connection system.
A fifth object of the present invention is to reduce the complexity of a connection system.
A sixth object of the present invention is to avoid using any microprocessors in a connection system in order to reduce cost and size.
In that regard, the present invention provides a connection system that uses time division to multiplex multiple signals. A plurality of signals are multiplexed together ranging from two to as many signals as desired. Input switches are grouped together to form a ladder multiplexer, such as a resistive multiplexer, that includes voltage and current muxing. A plurality of ladder multiplexers are joined together in a time division multiplexing scheme that operates continuously. An analog line may be added as a single channel. A marker pulse is used to signal the start of each time window to be divided for all the channels. Time division multiplexing is provided by a number of switching means. For simplicity this inventor has used analog switches to perform these functions. In the preferred embodiment an analog switch and a multiplexer integrated circuit (IC) are used to reduce the parts count. The preferred analog switch is manufactured and sold by Motorola, Inc. of Phoenix, Calif.